Earlier this month, I arranged to visit the wind research teams at Sandia National Lab and the National Renewable Energy Lab’s National Wind Technology Center, both of which are relatively nearby here in the southern Rockies. I’ve been following the work of many of these researchers for the past year or so—it was central to my 2012 Renewable Energy World conference paper and presentation on efforts to quiet turbines—and was very interested in learning more about their past, current, and future studies.

In particular, the Sandia team has recently built a Scaled Wind Farm Testing (SWiFT) facility, at which they’ll be studying wake interactions between turbines, and they’ve long been on the forefront of developing new materials and experimental active systems to reduce load strains caused by inflow turbulence. They’re also leading the development longer blades, which may have important noise implications. Their most exciting forward-looking project is a 5-year effort to re-activate development of vertical axis turbines, with the goal of moving toward 5-10MW scale vertical axis turbines for use offshore (this will be a 10-20 year project, if the first phase shows promise). Meanwhile, at NREL’s NWTC, lots of research has looked at the pinpointing the sources of sound on turbine blades, as well as advanced modeling of sound propagation in various atmospheric conditions. Researchers there have quantified the power-production trade-offs caused by wake interactions within wind farms, and are on the leading edge of new technology that might allow individual turbines to monitor incoming air flows and adapt their operations to minimize loads and noise. All of this research has intrigued me, because of the likely role of wakes and atmospheric turbulence in wind turbine noise levels, and in creating some of the more intrusive sound qualities that neighbors find hard to live with. My hope was to sit down with these researchers and learn more about their work, as well as draw on their experience to see whether they thought the turbulence factors they study to reduce stress on turbines may indeed also have an effect on the sounds.

As it turns out, they were also intrigued by such a dialogue, and both labs asked me to present their teams with a seminar on what I’ve been learning about community responses to turbine sound. Much of what I shared was new to them, and we had some great discussions. One of the central take-aways from both teams was that very little research has really looked at the acoustic effects of inflow turbulence, and there was universal agreement that this is an important area for future study (as a start, the SWiFT facility will incorporate some acoustic measurements). Many of them were especially interested in the varying sound quality of turbines, and the ways that this may trigger negative responses among neighbors; there was much speculation about the potential to identify the conditions that create the troublesome knocking, banging, thumping sounds, and perhaps adapt turbine operations to minimize or eliminate them. As I’ve long found in my interactions with academic and agency researchers, there was an easy openness and curiosity in both rooms, with many questions tossed around, and an excitement about studies they hadn’t seen before.

Good stuff and looking forward to your forthcoming review of the ongoing spat over controls to limit excess amplitude modulation (EAM) here at Den Brook in the UK: http://www.denbrookvalley.co.uk

Should the Den Brook developer win the day, our case law precedent set by the unique Den Brook AM noise conditions will be unjustly decimated. Worse still, ever increasing numbers of affected people will be left with little alternative other than to abandon their homes as the EAM problem escalates with increasing numbers of wind farms being developed in far too close a proximity to homes, schools etc. We know of more than 60 wind farms here in the UK where neighbours are badly affected by EAM noise intrusion especially during night-time periods.

What’s particularly disturbing is the UK wind industry continues with claims of EAM being so rare that they are left with little alternative other than to loop a 20-seconds recording to obtain a minutes worth of EAM for their analyses of the problem. Notwithstanding such attempts to mislead, and flying directly in the face of such industry claims, are a number of real-world, interactive recordings of EAM from a variety of UK sites that can be accessed here: http://www.masenv.co.uk/windfarms – look for the “Listening Room Experience”

One has to wonder how some of the ‘industry’ acousticians can sleep at night!

Atb
Mike

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